04 grand Cherokee Laredo 4.0L misfiring on all cylinders s

Asked by Sep 13, 2017 at 01:13 PM about the 2004 Jeep Grand Cherokee Laredo

Question type: Maintenance & Repair

04 grand Cherokee Laredo 4.0L is misfiring on all 6
cylinders but it doesn't do it all the time sometimes
it starts with out a problem and idols just fine other
times it idols rough and there is no warning lights
on. It sat for about 6 months before I bought it

5 Answers

Something I forgot to mention when it happens I can smell exhaust really strong it kinda smells like straight gas


Your check engine light may have been disabled, because it should definitely come on with all that going on. Let's assume it has been disabled... you can still check the codes by following a series of simple steps. (you'll have to look up the codes online or thru a part store) To get the codes to pop up put your Jeep in park and turn the engine off.... Turn key from "acc." to "run" and back a few times and the code(s) will appear on your odometer when it's in the "run" position (after a few times of turning the key back and forth) It only displays each code for a few seconds so be ready to snap a pic or jot down the digits it shows. Then you'll have to look up the number(s) to figure out what they mean, the codes themselves are meaningless since they don't tell you what they represent. If you have a service manual for your Jeep it may have a section definig the codes. If not Auto Zone or a quick Google search should tell you what you need. I would definitely check for codes before I'd start dumping money into it buying random parts because the issues you're having could be anything from plugs/wires, coil pack, injectors, Wiring to any of the above TSB on carbon buildup on valves that causes misfire codes Bad fuel (water, garbage etc) Fuel pressure probs (clogged filter, dying pump, regulator, or water in gas etc) Bad TPS ( a bad tps can cause voltage spikes that mess with the PCM causing it to throw random misfire codes) lean air/fuel ratio o2 sensor probs clogged catalytic convertor -(if it's this you may be able to tell by driving it about 30 mins or so a night (in a dark area) then looking underneath your Jeep. The catalytic converter and some of the exhaust pipe may glow red...and be very hot! That's one way to tell (trouble climbing hills is another dead giveaway) vacuum leak low compression caused by head gasket, rings, valve train etc So, yeah... that's not even a complete list of possible issues so you definitely want to get a reading on as many codes as you can before you start throwing money at it. Good luck.

I took it to advanced and had them check it he didn't tell me what codes it was giving but he did say that it was misfiring on all 6 cylinders


I'm leaning toward it being either the o2 sensors, (#1 cause of most check engine lights I see are 02 sensors or EGR valves) I'd check/clean spark plugs . Check on getting a fuel system cleaning... you could have some type of clog in your fuel system causing the fuel vapor to back up.

The fuel tank was almost completely empty when I got it and I was already planning on changing the spark plugs and coil rail but I'll check on the O2 sensor and EGR valve. I thought about running seafoam through it but I have never used it before

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